This invention relates to a portable medium which contains a CPU, a data memory, and an internal battery, such as a multifunctional IC card which can display the time and can also be used as an electronic calculator.
Multi-function IC cards containing a CPU, a data memory, and an internal battery, have been developed. Such IC cards, when used solely, serves as electronic calculators based on the functions of keyboard and display or as time pieces. When set to the terminal devices, it can transfer data to and from the terminal devices.
In such IC cards, the card holder can set and change the time if necessary. This fact allows it to be used as time pieces such as wrist-watches.
In such IC cards, since the time set can be changed, it is impossible to limit the effective period of the use of the IC card by making use of time, or to use as the key for encoding. Therefore, since the cards have different set times, it is impossible to execute appropriate processings common to these cards by using the time data of the time piece.
Additionally, in this type of IC card, a clock signal for driving the CPU is generated by a single oscillator. In some type of IC cards, the CPU clock signal is always generated; however, in most IC cards, the CPU clock signal is generated only when the CPU is used, in order to conserve battery power.
To restart the stopped oscillator, a power-on switch specially provided on the keyboard or a switch equivalent to it is pushed. However, when the oscillator is re-started, it takes some time before it is operating stably. Consequently, a signal input from any key will not be accepted until the oscillator is operating stably, which is a drawback.
Furthermore, the number of keys is increased. Additionally, the current consumption is incompletely reduced.